The invention relates to a memory-programmable control (SPS) for coupling to a data interface of a personal computer (PC), having means for operating the inputs and outputs of the SPS, the means including keys for tripping machine functions.
A memory-programmable control of this kind is already known from International Patent Application WO 97/03390.
In automation technology, manifold tasks in the industrial and private field are administered by using memory-programmable controls (SPS). The most important function elements of the known SPSs are a program memory and an SPS user logic (controller) with inputs and outputs. The SPS user logic includes a microprocessor as well as a data memory with memory regions, in particular for times, counters, flags, and process images. In the typical course of work, the SPS user logic, at the beginning of each cycle, calls up the signal states at the inputs of the SPS and sets a memory location (SPS flag), assigned to each input, to zero or one. In a subsequent program execution, the microprocessor accesses the process image of the inputs that is stored in memory and as a function of it processes the control instructions that are in the program memory. Via the outputs of the SPS, finally, signals are sent to the systems and machines that are to be controlled.
Besides the purely automatic mode of the SPS, however, again and again there is a need, for instance in manual operation, to trip certain machine functions using external user control means. Conventionally, the manual tripping of machine functions is done via a pushbutton matrix that is located on a machine control board of the SPS.
In this conventional SPS without a PC coupled to it, which is not an SPS of the generic type in question here, each pushbutton of the pushbutton matrix is connected to its own input of the SPS. Via the SPS user logic, these inputs are linked with outputs to the machine to be operated. In this way, actuating the pushbutton trips a machine function, such as the moving of a shaft. Safety requirements can readily be met, since the machine function is only active as long as the pushbutton is actuated. The signal loss of a “stop signal” for ending the machine function is precluded from the very outset in this connection, since the SPS flag corresponds directly to the voltage signal at the input. A disadvantage of this described conventional tripping by external pushbuttons connected directly to an associated SPS input, each pushbutton being allocated a single fixed meaning, is that both one pushbutton and one SPS input are needed for each machine function. As a result, the hardware is expensive, and the system is complicated to operate.
From the aforementioned WO 97/03390, it is known for an SPS to be coupled in a generic way to a conventional PC via a data interface, in order to be able to program and operate the SPS from the customary user surface of the PC, such as its keyboard and screen. As a result, machine functions can be tripped without additional external pushbuttons, but indirectly, with the interposition of the PC, via the keys of a conventional PC keyboard.
In conventional user surfaces such as PC keyboards, it is furthermore widely known, for instance by using a keyboard controller, to set up three different key levels, or in other words to make keys available on the PC keyboard whose meaning changes with the particular key level selected. From there, based on the known coupling of an SPS to a PC, the possibility arises of allocating a changing meaning for machine functions to at least some of the keys of the PC keyboard, and thus in terms of manual operation of a relatively large number of machine functions by an SPS to achieve economy in terms of hardware and make user operation simpler. In fact, however, with such provisions major safety concerns are involved, since when a PC key is pressed, what is forwarded to the SPS via the data interface is not a direct voltage signal but rather only data that represent the image of the key status, and this leads to the occupation of a memory unit in the SPS, or in other words the setting of an SPS flag, corresponding to the key status represented. The SPS user logic links this SPS flag without outputs to the machine. Any disruption within the communications path from the PC to the SPS would therefore undo what is only a data connection between the key and the machine function. In the event of a disruption, the most recent key status in the SPS would stay active. In the “key ON” state, the change of state to “key OFF” could not be transmitted to the SPS; that is, a machine that has been set in motion for instance would continue to move onward in an unwanted way.